Army's Paeon is a series of songs available to Bards in Final Fantasy XI. There are five versions of Army's Paeon, I through V. They have an effect similar to Regen on multiple targets. Army's Paeon is considered a different status effect though, and it will stack with the effect of Regen. Since a character can be affected by up to two songs, a bard can place two Paeons on the same player so long as they have a different number.
A paean is a song of praise or triumph.